Drum washers have been typically configured by an exterior housing containing a tub which further contains a drum being driven in rotation by a motor provided outside the tub. The tub is disposed above the bottom panel of the exterior housing through an elastic support of a suspension which is provided with a damper configured to reduce the oscillation of the tub caused by the oscillation of the drum.
FIG. 29 shows one example of a damper primarily configured by cylinder 1 and shaft 2 inserted into cylinder 1. Cylinder 1 is connected to the tub not shown by connecting member 3 provided on its upper end, whereas shaft 2 is connected to the bottom panel not shown of the exterior housing by connecting portion 2a provided on its lower end.
Cylinder 1 is cylindrical in form and contains coil 4 being stored in bobbin 5 and coil 4 is disposed so as to surround shaft 2. Inside cylinder 1, ring-shaped yokes 6 and 7 made of magnetic material are disposed on both axial or upper and lower ends of coil 4. Magnetic circuit M is established between yokes 6 and 7, shaft 2, and cylinder 1. More specifically, magnetic circuit M defines a closed circuit of magnetic flux path which is generated by the conduction of coil 4 and configured by shaft 2—upper yoke 6—cylinder 1—lower yoke 7—shaft 2.
Between upper yoke 6 and 7, coil 4, and shaft 2, magnetic viscous fluid also referred to as MR fluid is filled. Magnetic viscous fluid 8, when subjected to magnetic field, varies its viscosity depending on the strength of the magnetic field and comprises, for example, a mixture of ferromagnetic particles such as iron and carbonyl iron dispersed in oil. Application of magnetic field causes the ferromagnetic particles to form a chain of clusters that results in an increase in viscosity.
Inside cylinder 1, seal 9 is disposed axially outward of or below lower yoke 7. Seal 9 prevents leakage of magnetic viscous fluid 8 from the space provided between yokes 6 and 7, coil 4, and shaft 2 which is also referred to as magnetic viscous fluid filling portion 10.
Cylinder 1 further contains lower bearing 11 disposed axially outward of or below seal 9 and upper bearing 11 disposed axially outward of or above upper yoke 6. These bearings 11 and 12 support shaft 2 to allow relative reciprocating movement in the axial direction.
Further inside cylinder 1, reserved space 13 is provided above upper bearing 12. A predetermined amount of magnetic viscous fluid 8 is stored in this reserved space 13 while also filling the space between reserved space 13 and magnetic viscous fluid filling portion 10. The upper end of shaft 2 is located within reserved space 13 and thus, is placed in contact with magnetic viscous fluid 8.
Damper 14 is configured as described above.
Immediately above connecting portion 2a of shaft 2 located below and outside cylinder 1, spring receiving plate 15 is attached. Between spring receiving plate 15 and lower bearing 11, spring (compression coil spring) 16 is provided which is capable of expanding and contracting. Suspension 17 is configured in the above described manner and provides elastic support to the water tub.
When the operation of a drum washer configured as described above is started, the rotation of the drum containing laundry oscillates the tub mostly in the up and down direction. In response to the up and down oscillation of the tub, cylinder 1 constituting suspension 17 and being connected to the tub, oscillates up and down around shaft 2 with extension/contraction of spring 16 along with upper bearing 12, upper yoke 6, coil 4, lower yoke 7, seal 9, and lower bearing 11.
When cylinder 1 oscillates up and down around shaft 2 along with the above described components, magnetic viscous fluid 8 filled between shaft 2, yoke 6 and 7, and coil 4 exerts damping force through frictional resistance imparted by the viscosity to reduce the degree of oscillation of the tub.
The conduction of coil 4 further generates magnetic circuit M which significantly increases the viscosity of magnetic viscous fluid 8 residing in the path of magnetic flux which includes, in particular, the space between shaft 2 having relatively high magnetic flux density and upper yoke 6, as well as the space between lower yoke 7 and shaft 2, thereby increasing the imparted frictional resistance. The damping force is thus increased by the increase in the frictional resistance during the up and down oscillation of cylinder 1 oscillating along with the above described components, especially coil 4, upper yoke 6, and lower yoke 7.
Coil 4 is configured to control the viscosity of magnetic viscous fluid 8 by generating a magnetic field corresponding to the level of the flowing current, meaning that the generated magnetic field varies with the level of current to variably control the viscosity of magnetic viscous fluid 8.
In another typical related example, the damper is configured to obtain a certain damping force by suppressing the flow of the magnetic viscous fluid caused by the relative movement of the cylinder and the shaft, and thus, produces the damping force in a different way as compared to the above described damper in which the damping force is imparted by the frictional resistance originating from the viscosity of magnetic viscous fluid 8 filled in the magnetic viscous fluid filling portion 10 when cylinder 1 and shaft 2 are relatively oscillated in the up and down direction.
In the related example shown in FIG. 29, seal 9 that prevents leakage of magnetic viscous fluid 8 from magnetic viscous fluid filling portion 10 is provided only on the lower side of cylinder 1, and the upper side of cylinder 1 stores magnetic viscous fluid 8 in reserved space 13. As a result, even when magnetic viscous fluid 8 leaks into reserved space 13 through the space between upper bearing 12 and shaft 2 from magnetic viscous fluid filling portion 10 due to heat expansion and oscillation, etc., magnetic viscous fluid 8 will go back to magnetic viscous fluid filling portion 10 from reserved space 13 when the temperature drops. Thus, it has been presumed that the density of magnetic viscous fluid 8 of magnetic viscous fluid filling portion 10 is maintained and therefore, no degradation occurred in the damping force.
However, as magnetic viscous fluid 8 deteriorates, its viscosity becomes greater and transforms into a margarine like state. Magnetic viscous fluid 8, when increased in viscosity, sticks onto the inner wall of reserved space 13 and stays there as shown in the double dot chain line in FIG. 6 when it leaks into reserved space 13. This will not allow the space between upper bearing 12 and shaft 2 to be sealed with magnetic viscous fluid 8 and as expansion and contraction of magnetic viscous fluid 8 is repeated in such state, air within reserved space 13 is introduced into magnetic viscous fluid filling portion 10 from the space between upper bearing 12 and shaft 2, thereby reducing the density of magnetic viscous fluid 8 within magnetic viscous fluid filling portion 10 and consequently degrading the damping force.